In complex molding technology, the mold gates which are used to control the flow of molding compound into a mold chamber may be controlled by pressure and temperature sensors. If desired, computer-operated adjustment of the gates may be utilized by a feedback loop from the pressure and temperature sensors to the control gates. However, for many purposes, such a system has been found to have insufficient sensitivity, while being excessively complex.
Another problem of mold gating which is commonly encountered in the various structures of the prior art is gate freeze, in which the molding compound obstructs the gate.
When a very small gate is used in order to obtain better control of the flow, undesirable levels of material shear and gate stresses can occur, which can actually degrade or decompose the molding material, due to the tremendous kinetic forces applied on the material as it is forced through the gate.
Similarly, other problems which are encountered in molding may include material suck-back through a gate which stays open too long, or gate drool. Also, the problem of balancing multiple gates in a molding process so that desired flows pass through each of them can be a major technical problem.
In accordance with this invention, all of the above problems can be greatly reduced or eliminated by means of the hydrostatic gate of this invention, which operates spontaneously in a pressure-sensitive manner to permit the flow of molding compound into the mold chamber through a relatively wide orifice, to avoid the undesirable shear and stresses on the molding compound. At the same time, the gate shuts off quickly and spontaneously when the back pressure in the mold chamber essentially equals the pressure in the molding compound inlet conduit, for high speed injection molding.
Similarly, should the pressure equalization merely be transient for any reason, for example, shrinkage in the mold or the need for "packing out" the mold, the hydrostatic gate of this invention can spontaneously reopen to provide further molding compound to the chamber. The result of this is a major improvement in molding technology, with the elimination of multiple technical problems in a wide variety of molding operations, including complex multiple gate molding operations.